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| 2. |
- Hill, V., et al.
(författare)
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The Hamburg/ESO R-process Enhanced Star survey (HERES)
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 607
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Tidskriftsartikel (refereegranskat)abstract
- We report an abundance analysis for the highly r-process-enhanced (r-II) star CS 29497-004, a very metal-poor giant with solar system T-eff = 5013 K and [Fe/H] = -2 : 85, whose nature was initially discovered in the course of the HERES project. Our analysis is based on high signal-to-noise ratio, high-resolution (R similar to 75 000) VLT/UVES spectra and MARCS model atmospheres under the assumption of local thermodynamic equilibrium, and obtains abundance measurements for a total of 46 elements, 31 of which are neutron-capture elements. As is the case for the other similar to 25 r-II stars currently known, the heavy-element abundance pattern of CS 29497-004 well-matches a scaled solar system second peak r-process-element abundance pattern. We confirm our previous detection of Th, and demonstrate that this star does not exhibit an "actinide boost". Uranium is also detected (log is an element of (U) = -2 : 20 +/- 0 : 30), albeit with a large measurement error that hampers its use as a precision cosmo-chronometer. Combining the various elemental chronometer pairs that are available for this star, we derive a mean age of 12 : 2 +/- 3 : 7 Gyr using the theoretical production ratios from published waitingpoint approximation models. We further explore the high-entropy wind model (Farouqi et al. 2010, ApJ, 712, 1359) production ratios arising from different neutron richness of the ejecta (Y-e), and derive an age of 13 : 7 +/- 4 : 4 Gyr for a best-fitting Y-e = 0 : 447. The U/Th nuclei-chronometer is confirmed to be the most resilient to theoretical production ratios and yields an age of 16 : 5 +/- 6 : 6 Gyr. Lead (Pb) is also tentatively detected in CS 29497-004, at a level compatible with a scaled solar r-process, or with the theoretical expectations for a pure r-process in this star.
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| 3. |
- Landstrom, U, et al.
(författare)
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Effect on truck drivers' alertness of a 30-min. exposure to bright light: a field study
- 2004
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Ingår i: Perceptual and motor skills. - : SAGE Publications. - 0031-5125 .- 1558-688X. ; 98:33 Pt 1, s. 770-776
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Tidskriftsartikel (refereegranskat)abstract
- Reduced alertness is common during night driving. Light treatment may constitute one countermeasure to reduce sleepiness. To test this idea six professional drivers participated in this study in which they self-administered a 30-min. light treatment during a break in the middle of a night drive of about 9 hours. Two experimental conditions were used, including light exposures with a light box and a light visor. There was a control condition. Alertness was measured on a 100-mm visual analogue scale. No significant effect of light was found, but ratings of sleepiness increased significantly through the night drive. The experimental light treatment was not correlated with any increased wakefulness compared to the drivings where no extra light exposures were carried out.
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| 4. |
- Perez, A. E. Garcia, et al.
(författare)
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A new sample of extremely/ultra metal-poor stars
- 2008
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T133, s. 014036-
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Tidskriftsartikel (refereegranskat)abstract
- A sample of 30 very metal-poor stars from the Hamburg-European Southern Observatory (ESO) objective-prism survey have been observed at high spectral resolution at the Very Large Telescope (VLT) using the Ultraviolet and Visual Echelle Spectrograph (UVES). Two of the observed stars are very interesting not only because of their very low iron content, approximately four orders of magnitude lower than the solar value, but also because we detected the neutral lithium resonance line at 670.8 nm. Hydrogen lines suggest that the two observed stars have effective temperatures around 6000-6250K and according to isochrones, they are either on the main-sequence or on the subgiant branch, in which case they would probably be the most metal-poor dwarfs or warm subgiants with lithium detections known. These detections would allow to determine more accurately the slope of the trend of the lithium abundance with [Fe/H] than was possible with samples of unevolved stars restricted to higher metallicities.
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